Treatment of uranium surfaces



2,872,389 TREATMENT GE URANIUM SURFACES SerialNo. 718,623 9'Claims. (Cl. 204-15 N D w n This. inventionrelatesto an improvement in methods forelectroplating metals upon uranium surfaces. More particularly the invention relates to an improved method of preparing uranium surfaces for electroplating.

The adhesion of electrodeposited coatings to a base metal depends to a greatextent on intimate contact of the coating and the base. metal. .In order for a crystalline deposit to be continuous, each layer of atoms must be influenced by the orientation of the atoms of the preceding layer. Obviously for the growth of an adhered deposit it is necessary that the deposited metal be in intimate. atomic contact with the base metal crystalline structure. Under these conditions, the crystals of the deposited layer may be formed as a direct extension of the crystals in the base metal. Such a coating becomes an integral part of the article being plated.

The above theory of electroplating has been found to be of fundamental importance in the plating of adherent coatings on uranium. Absolute cleanliness of the metal surface priorto plating can bedefined as that condition whichpermits the structure of the base metal to be continued by. electrodeposition. The presence of grease, oxides or other extraneous materials markedly reduces adhesion. In most platingwork, a roughened surface such as is produced by. sandblasting improves the bond between coating and base metal.

The adherenceof plating metals on uranium is thus dependent upon the intimate contact of crystals of the plated metal with the crystals of the base metal, uranitun.

When such intimate contact is achieved, it is believed thatv the initial crystals of the depositedlayer of, for example, r

nickel or copper, are-formed as direct extensionsof the crystals of uranium so that the plated coating becomes an integral part of the specimen being plated. Thus, in addition to the usual cleaning and pickling procedures to insure the removal of grease and heavy oxide films, uranium must be. given a special pretreatment in which the essential factor involved appears to be attacking of the base metal uniformly to remove crystals distorted by surface-working, so that the surface exposed for plating has the basic crystalline structure of the base metal. After such treatment, the electroplate takes on its adherence 2,872,38 Patented ch. 3, 1959 2 vide a process for treating uranium surfaces to render them suitable for the electroplating thereon of firmly bonded adherent coatings.

It is a more specific object of the invention .to provide an anodizing bathfor anodic treatment of uranium to produce such surfaces priorto electroplating.

Generally the objects of this invention are accomplished by anodizing the uranium surface in a bath of a solu .tion of phosphoric acid containing hydrochloric acid.

The methods that have proven successful for the deposition of adherent electroplates to uranium involve anodizing of the uranium in solutions containing chloride ions. Hydrochloric acid reacts very violently with uranium even by simple immersion at room temperature. However, uninhibited solutions of hydrochloric acid have not proven satisfactory for pretreating purposes for the .following reasons: (1) a very non-uniform surface is produced; (2) the reaction once started is diflicult. to control; and (3) adherent electroplates are not found to be obtained on surfaces thus prepared.

Anodizing of uranium surfaces in phosphoric acid, H PO has been found to cause electropolishing of the uranium surfaces, and electroplates do not adhere well to uranium after such treatment.

In the present invention the anodizing is done with a solution of phosphoric acid into which hydrochloric acid has been introduced. This is found to produce a highly desirable result which is not obtainable from either of the above substances alone. By anodizing the uranium in a proper solution of the black deposit may be formed on the uranium. This black deposit or film may be removed by a short dip in nitric acid and the resulting surface has a smooth grey appearance of very fine texture which is found to be capable of being electroplated with such metals as nickel and copper with an excellent bonding of the deposited plate to the uranium base.

The exact theory which accounts for this result is not known. The combination of the electropolishing effect of the phosphoric acid and the pitting action of the hydrochloric acid seems to result in a controlled attack on the surface of the metal which renders the electroplate firmly adherent.

In the following Table I are shown the results of a series of experiments designed to determine the optimum concentrations of phosphoric acid and hydrochloric acid. The standard for determining the optimum results was of necessity highly empirical. The test was performed by electroplating nickel on the surfaces anodized in the various baths shown in the table and thereafter filing an edge of the sample and examining the filings for separation of nickel. plate and base metal. The adhesion qualities of the platings obtained were rated on the basis of 10 for the best results obtained, decreasing numerals representing decreasing adherent qualities of the platings.

by virtue of following the fundamental crystalline contour of the base metal.

It is the principal object of the present invention to pro- It appears from the above table that optimum results. are obtained in cleaning the uranium surface preparatory to electroplating by using a solution of phosphoric acid.

above substances, a uniform temperature of the bath and of current density in the anodizing treatment. The results of these tests are shown in Table II which follows, the numerals indicating the quality of the bond achieved in plating nickel as in Table I.

Table 11 Current density, amperes per square inch Temperature Here again, although the ratings shown in the table do not allow exact determination of the optimum conditions, it has been found that a bath temperature of approximately 35 to 45 C. and an anodizing current density of approximately 0.5 ampere per square inch of surface represent optimum conditions. This determination was likewise made of the basis of sub-gradations which are not shown in the table. It has been found that the optimum time for the anodizing treatment is ten minutes.

A complete procedure which has been found to produce an excellent electroplating of such metals as nickel and copper on uranium surfaces is as follows:

The surface is first cleaned of grease in a solvent such as carbon tetrachloride by rinsing and wiping. The major portion of the oxide film is then removed by dipping in an acid such as 70 percent nitric acid for a time of the order of 1 /2 minutes. The uranium is then rinsed in tap water. It is then anodized in the bath consisting of a 50 percent solution of phosphoric acid containing cc. per liter of concentrated hydrochloric acid for ten minutes at a temperature of 40 C. with a current density of 0.5 ampere per square inch of surface.

The uranium is then again rinsed in tap Water and the film formed in the anodizing is'then removed by dipping for a short time, of the order of 20 to 50 seconds, in 70 percent nitric acid. After a further rinse the surface is electroplated.

What is claimed is:

1. In the process of electroplating uranium, the step of anodizing the surface of the uranium in a bath comprising a solution of approximately 50 percent by weight of phosphoric acid containing about 20 cc. per liter of concentrated hydrochloric acid at a temperature of about to C. for approximately 10 minutes, the anodizing current density being about 0.5 ampere per square inch of said surface.

2. In a process of cleaning a uraniumsurface, the step of anodizing the surface of the uranium in a bath comprising a solution of approximately 20 percent to 60 percent by weight of phosphoric acid containing about 20 cc. per liter of concentrated hydrochloric acid at a tem perature of about 35 to 45 C; for approximately 10 minutes, the anodizing current density beingabout 0.5 amperes per square inch of said surface.

3. In a process of cleaning a uranium surface,'the.

step of anodizing the surface of the uranium in a bath comprising a solution of approximately 20 percent to 60 percent by weight of phosphoric acid containing approximately 20 to cc. per liter of concentrated hydrochloric acid at a temperature of about 35 to 45 C.,. the anodizing current being in the range of 0.125 to 1.0 ampere per square inch of said surface. 4. In a process of treating uranium, the step of anodizing the surface of theuranium in a bath comprising a solution of approximately 20 percent to 60 percent by weight of phosphoric acid containing approximately 203 to 100 cc; per liter of concentrated hydrochloric acid.

5. In a process of treating uranium, the step of anodizing the surface of the uranium in a bath comprising" a solution of from 20 to 60 percent by weight of phosphoric acid containing approximately 20 cc. per liter of concentrated hydrochloric acid.

6. In a process of treating uranium, the step of anodizing the surface of the uranium in a bath comprising a solution of from 20 to 60 percent by weight of phosphoric acid containing approximately 20 to 100 cc. per liter of concentrated hydrochloric acid.

7. In a process .of treating uranium, the step of anodizing the surface of the uranium in a bath comprising a solution of approximately 50 percent by weight of phosphoric acid containing 20 to 100 cc. per liter of con-.

centrated hydrochloric acid.

8. In a process .of treating uranium, the steps of anodizing the surface of the unanium in a bath comprising a solution of approximately 20 to 60 percent by weight of phosphoric acid containing 20 to 100 cc. per liter of concentrated hydrochloric acid, and then dipping the I treated uranium shortly in nitric acid.

9. A process of treating a uranium surface comprising the steps of removing grease, removing oxide film by an acid dip, anodizing in a bath'containing from 20 to 60 percent by weight of phosphoric acid and from 20 to 100 cc. per liter of concentratedhydrochloric acid, removing the film resulting from anodizing and thereafter electroplating upon said surface.

References Cited inthefileof this patent UNITED STATES PATENTS 1,658,222 Burns Feb. 7, 1928 1,933,319 Driggs et a1. Oct. 31, 1933 2,133,255 Rogers Oct. 11, 1938' OTHER REFERENCES Transactions of the Electrochemical Society, vol. 66 (1934), pp. 40, 41. 

1. IN THE PROCESS OF ELECTROPLATING URANIUM, THE STEP OF ANODIZING THE SURFACE OF THE URANIUM IN A BATH COMPRISING A SOLUTION OF APPROXIMATELY 50 PERCENT BY WEIGHT OF PHOSPHORIC ACID CONTAINING ABOUT 20 CC. PER LITER OF CONCENTRATED HYDROCHLORIC ACID AT A TEMPERATURE OF ABOUT 35* TO 45* C. FOR APPROXIMATELY 10 MINUTES, THE ANODIZING CURRENT DENSITY BEING ABOUT 0.5 AMPERE PER SQUARE INCH OF SAID SURFACE. 